Magnetism(Review)
What do we know about magnets? 2 Magnetically opposite poles: North Pole and South Pole Like poles repel and Opposite poles attract “We’ll get back to this later”
What types of things do magnets attract? “Do magnets attract all metals?” Magnets only attract objects made of iron, cobalt, or nickel!! These metals are called the “Iron Triad” See Periodic Table You can also only make a magnet out of these 3 metals. Those “rubber” magnets have iron, cobalt or nickel in them.
Magnetic Domains The molecules of most substances have no orientation to them. In a magnet, the molecules align themselves in a very specific pattern.
Magnetic Field Surrounding all magnets is a magnetic field. Magnetic Field is the area surrounding a magnet where the magnetic force acts. Magnetic Field Lines
The North Pole is the pole that the magnetic field lines move out of. The South Pole is the pole that the magnetic field lines move into.
Magnetic Field Lines Magnetic Field lines always move out of the North end and into the South end!!
Magnetic Field Lines of Interacting Magnets Lines of Attraction Lines of Repulsion
What happens if you break a bar magnet in half? Mr. Eidson You get 2 bar magnets both with a North and a South pole!!
Breaking a Bar Magnet
Is there a relationship between electricity and magnetism Is there a relationship between electricity and magnetism? Let’s see what I discovered!!! Hans Christian Oersted
Oersted’s Law The flow of electricity through a wire conductor produces a magnetic field around the wire.
2 things affect the strength of a magnetic field: Amount of current Increase current = increase strength Decrease current = decrease strength # of coils of wire More turns of wire = more strength Less turns of wire = less strength
If you take an iron core and insert it into a coil of current carrying wire, you have a temporary magnet called an electromagnet!!
Strength of an Electromagnet 2 things affect the strength of an electromagnet(same 2 things that affect the strength of a magnetic field): Amount of Current # of turns of wire(# of coils)
Uses of Electromagnets Electric Meters: because of their ability to detect current(only work when there is one), electromagnets are used in a variety of electric meters. Ammeter—measures current Wired in series Voltmeter—measures voltage Wired in parallel Galvonometer—”detects” current
Uses of electromagnets(cont.) Motors Use electromagnets to convert electrical energy into mechanical energy An electromagnet turns inside a permanent magnet
Motors
Faraday and Henry discovered that moving a wire through a magnetic field, or moving a magnetic field through a coil of wire “induced” a current on the wire!! Electromagnetic Induction—process in which moving a wire through a magnetic field produces a current on the wire.
….produces a current on a wire. “Did we just “create” electricity” Generators—use electromagnets to convert mechanical energy into electrical energy.
Generators
Are you talking about me? Other Uses of electromagnets: Transformers Are you talking about me? Not this Kind!!!!
Alternating vs. Direct Current Alternating Current Direct Current Current alternates, one direction, then the other. Current only goes in one direction. Plug it in, Plug it in!!
Transformers Used to increase or decrease the voltage of alternating currents.
Transformers Consist of 2 coils of wire. Primary Coil Alternating current enters Secondary Coil Alternating current leaves It’s the difference in the number of turns of wire on each coil that causes the voltage the change.
2 Types of Transformers Step-up Transformer Step-down Transformer Increase voltage Primary more turns than secondary Step-down Transformer Decrease voltage Secondary more turns than primary
Math of a Transformer:
A step-up transformer has 400 turns on its primary coil and 600 turns on its secondary coil. If the primary coil is supplied with 120 V of alternating current, what will be the secondary (output) voltage? ns= 600 turns np= 400 turns Vs= ? Vp= 120
Example #2
Example #3
Independent Practice: